1. Field of the Invention
This invention relates to a steel multi-layer composite molded structure, more particularly to a composite structure having a plastic foam material chemically bonded by silane directly to a carbon steel or stainless steel substrate to impart resistance to delamination when subjected to impact and/or thermal shock.
2. Background of the Prior Art
In the development of bathroom and kitchen fixtures, as well as whirlpool tubs and other composite articles, the porcelain-cast iron fixtures have gradually been replaced by lighter and more resilient composite structures. One of the difficulties with the porcelain-cast iron and enameled fixtures has been their susceptibility to impact damage and their extreme weight which cause great difficulties in moving and installing large fixtures such as sinks, bathtubs and whirlpool tubs. The porcelain cast-iron fixtures did have the advantage of having a very solid feel and high weight bearing capability.
Initial attempts by the industry to replace these porcelain cast-iron fixtures proved difficult. The thin stainless steel fixtures did not have the solid feel or structural strength required for large articles such as sinks bathtubs and whirlpool tubs. The early composite structures have a plastic, hollow feel and would deform, crack, chip or delaminate when subjected to impact, thermal shock or the weight of a typical bather. Also, these composite structures would often delaminate, crack, craze or chip when subjected to impact from the outside of the structure during manufacturing, transportation and installation of the fixture.
One attempt to make a lightweight metallic composite structure is exemplified in U.S. Pat. No. 3,496,058 which describes the use of a semi-elastic layer containing particulate material, such as sand, applied to one side of an aluminum sheet To this semi-elastic layer, a plastic foam is applied. The aluminum is difficult to form into a resilient structure and can be easily dented and deformed when subjected to impact or structural stress. Therefore, the use of this type of aluminum composite would be impracticable in the manufacture of plumbing fixtures due to its lack of structural integrity, the difficulty of molding aluminum sheets into articles, and the susceptibility of aluminum to pitting and corrosion.
One successful solution to these problems is disclosed in U.S. Pat. No. 4,664,982 to Genovese et al. the disclosure of which is incorporated by reference herein It discloses a composite enameled steel fixture which has both the look and feel of the earlier porcelain cast-iron fixtures. The composite structure is light, has high structural strength, and resists delamination, chipping and denting due to impact or thermal shock. The composite structure is formed from a steel shell, enameled on both its finish and non-finish sides The shell is used as part of a mold to form a layer of reinforced foamed plastic by Reaction Injection Molding ("RIM"), or by Reinforced Reaction Injection Molding ("RRIM") processing on the non-finish side The reinforced foamed plastic is chemically bonded to the enameled steel non-finish side by the action of silane. Silane is a coupling agent which creates chemical linkages between the SiOH groups in the enamel and the reinforced foamed plastic to form the laminate The composite structure possesses excellent physical and mechanical properties as a result of the chemical bonding of the reinforced foamed plastic layer to the enamel bonded to the steel shell. The structure, however, has two drawbacks The first, is that the steel article must be coated with enamel on its outer, non-finish side prior to lamination The second, is that the delamination resistance of the article is limited by the strength of the bond between the enamel layer and the steel shell layer, which is weaker than the bond created by silane between the enamel layer and the reinforced foamed plastic layer.
An alternative approach to these problems was to replace the enameled-steel shell with a polymeric, cosmetic surface layer and binding that layer directly to a foamed plastic substrate, i.e. a cross-linked isocyanate-modified thermosetting unsaturated polyester foam resin to provide a high impact strength, delamination-resistant structure. Methyl methacrylate and commercially available adhesive THIXON 416, manufactured by Whittaker Corp., West Alexandria, Ohio, which contains a blend of 65% solvents, 35% solids including polyurethane phenolic and epoxy resins, is used as a primer to cross-link and chemically bond the polymeric cosmetic layer with the isocyanurate groups in the foamed plastic while the plastic is cured. This approach is disclosed in U.S. Pat. Nos. 4,844,944 and 4,844,955, both to Grafe, et al., the disclosure of which is incorporated by reference herein. Thus, lightweight and durable plumbing fixtures, including bathtubs, shower receptors, lavoratories, sinks, etc. could be formed utilizing this method. Although these structures are light and delamination-resistant, they do not have the same sound, feel and texture as the prior porcelain-coated cast-iron structures or the enamel coated composite described in U.S. Pat. No. 4,664,982.
Accordingly, it is an object of the present invention to provide a stainless steel or enamel coated carbon steel structure which has the feel of a porcelain-coated cast iron fixture without the weight and delamination problems associated with such structures
It is also an object of the present invention to provide a composite enameled carbon steel or stainless steel structure which does not require an enamel coating on its non-finish side and has a RIM or RRIM formed relatively thick, reinforced, foamed plastic layer bonded to its non-finish side to provide a fixture which is highly resistant to delamination.
Another object of the present invention is to provide a plastic backed enameled-carbon steel or stainless steel plumbing fixture that is resistant to chipping, cracking, crazing, delamination or deformation when subjected to impact from either the finish or non-finish side, as when compared to presently available porcelainized cast-iron, enameled-carbon steel or composite plumbing products of comparable weight and gauge.